1. Field of the Invention
The present invention relates to a method and apparatus for measuring the water level in a boiler; and more particularly, the present invention relates to a method and apparatus for measuring the water level in a boiler using an ultrasonic level gauge and control device.
2. Brief Description of Related Art
In current techniques for water level gauge and control for a boiler or a hot water tank, a tubular sight glass mounted on the outside of the boiler and a water level switch at each end of the boiler control water levels are the most commonly used means for most residential, commercial or industrial applications. Due to the harsh working conditions of high temperature, high pressure, high humidity and condensate, and turbulent water surface while boiling, most techniques including some ultrasonic level measurements for a liquid tank through either an air path approach or a water path approach might be unfeasible and impractical for this specific application.
Different from most conventional applications for ultrasonic liquid level measurements at a liquid tank, the worst scenarios for a boiler application case are steamy condensate and turbulent water surfaces while boiling, as well as high pressure and temperature. The sound path that goes through the air from the top to the water surface in a boiler by using an air-coupled transducer will be ruined soon after the steam and condensate build up in the path when the water is boiling. On the other hand, instead of being reflected back to the transducer for the water path approach, almost all sound energy will be scatted away by the chaotic boiling water surface. The reason for that is mainly due to the wavelength or the center frequency of the sound which is used here. The shorter the wavelength, the more scattered the waves are by an uneven surface and the less the wave energy is reflected back. Different from an air-path approach with the transducer center frequencies ranging from 22 to 150 kHz, in the water path approach, a slightly higher frequency ranging from 0.5 to 2.25 MHz has to be used in order for sounds to penetrate through the wall thickness of the boiler and propagate in the water. Hence, based on this understanding in the prior art, there is no assurance at all for the ultrasonic water level measurements to be successful in a boiler.
In view of this, there is a need in the industry to solve the aforementioned problem in the art.